As an electronic member wherein an electrode is formed on a silicon semiconductor substrate, known is a solar cell element as disclosed in Japanese Patent Application Laid-Open Publication No. 2000-90734 (Patent Document 1) or Japanese Patent Application Laid-Open Publication No. 2004-134775 (Patent Document 2).
FIG. 1 is a view schematically showing a generally sectional structure of a solar cell element.
As shown in FIG. 1, the solar cell element is formed, using a p type silicon semiconductor substrate 1 having a thickness of 200 to 300 μm. An n type impurity layer 2 having a thickness of 0.3 to 0.6 μm is formed on the side of a light-receiving face of the silicon semiconductor substrate 1, and an antireflection layer 3 and grid electrodes 4 are formed thereon.
An aluminum electrode layer 5 is formed on the backside of the p type silicon semiconductor substrate 1. The aluminum electrode layer 5 is formed by applying a paste composition composed of aluminum powder, glass frit and an organic vehicle by screen printing or the like, drying the composition and then firing the resultant at a temperature of 660° C. (the melting point of aluminum) or higher for a short time. At the time of this firing, aluminum diffuses into the p type silicon semiconductor substrate 1, thereby forming an Al—Si alloy layer 6 between the aluminum electrode layer 5 and the p type silicon semiconductor substrate 1 and simultaneously forming a p+ layer 7 as an impurity layer based on the diffusion of aluminum atoms. The presence of this p+ layer 7 gives the BSF (back surface field) effect of preventing electrons from being recombined and improving the efficiency of collecting generated carriers.
As disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 5-129640 (Patent Document 3), the following solar cell element is put to practical use: a solar cell element wherein a backside electrode 8 composed of an aluminum electrode layer 5 and an Al—Si alloy layer 6 is removed with an acid or the like and a collecting electrode is newly made from a silver paste or the like. However, it is necessary to dispose of the acid used to remove the backside electrode 8. Due to the removing step, there are caused problems such that the process becomes complicated. In order to avoid such problems, recently, a solar cell element has been frequently constructed in the state that the backside electrode 8 is left and used, as it is, as a collecting electrode.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2000-90734
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2004-134775
Patent Document 3: Japanese Patent Application Laid-Open Publication No. 5-129640